Investigation of Ecology on Four Sites on the River Nar

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Investigation of Ecology on Four Sites on the River Nar

Introduction

“The environmental conditions change along the river. These conditions affect the diversity of species found at the different sites.”

Site 1- Kings Lynn

The first site we visited was situated on the river Nar just 400 meters from the Great Ouse and 1km from the sea. There are varying flow rates on this stretch of the river due to a sluice gate, which is controlled automatically. When the tide comes in the gates are closed, which prevents water from coming in therefore the flow rate slows down and the water becomes shallower. When the gates are open the flow rate increases and the site gets deeper. Due to the inflow of seawater the section gets brackish, this will cause osmotic problems for fresh water animals.

There is a pumping station situated near the site, which may pump industrial waste like heavy metals, oil, into the river also, road surface pollution and fertilisers from upstream are present in the river.

Site 2- Kings Lynn

This site is situated further down stream. There is no flow rate and no tidal influence. There is a huge population of surface algae, which prevents the penetration of light and the absorption of oxygen. Therefore there is less oxygen in the river and this will affect the fresh water species and plant life found here.

Site 3- High Bridge

Fields of sugar beet, potatoes and cereal crops surround this section of the river. These fields receive fertiliser, some of which may be washed in to the river. The water is above land level therefore every year the land gets waterlogged and the water is removed by being passed back into the river, therefore there is a greater agricultural influence in the river. The river has been straightened so the water flows more efficiently. It is also periodically cleaned i.e. vegetation and silt is removed. This is going to have an effect of the species found because there will be less vegetation therefore lower amount of oxygen available therefore less food therefore less shelter therefore fewer species. Algae present due to the presence of nitrates and phosphates present in the fertilisers passed into the river from he surrounding fields. The algae will also deplete the amount of oxygen present therefore there will be less available for the invertebrates.

Site 4- Castle Acre

This site is situated near the source of the river. It is a hilly part and contains l a large amount of calcium carbonate that may be used by invertebrates in the synthesis of exoskeletons. The water is filtered through chalk therefore the condition are alkaline and very cold. The water is shallow and fast flowing.  The water will contain low amounts of phosphates and nitrates because the surrounding fields under go low intensity farming.

The variable that will be taken into account include the flow rate, depth of water, amount of nitrates, phosphates, ammonia present in the water, the temperature, the amount of pollution from the surrounding areas, biological oxygen demand and the pH.

Plan / method

When carrying out this investigation, I will proceed to do the following:

Take water samples from each different site and determine the relevant amounts of different species present and their frequency. Give a description of each site and measure the following environmental factors

  1. the flow rate
  1. the oxygen levels at each different site in mg/l
  1. test a sample of water for the pH and temperature
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  1. record all the species present
  1. the temperature
  1. test for nitrates, phosphates and other minerals

The results for this investigation were obtained by following the method below.

A sample off water was collected in a sample tray.  The sampling net was placed in the water against the current and moved in a joggled motion, ensuring to dislodge as many samples of as many species as possible. The kick search method may also be used in shallow water with a fast current (castle acre). After the sample was collected, it was carried up to the tray ...

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